'How I Met Your Mother' Preview: Seth Green and Alyson Hannigan Reunite on "The Final Page"

'How I Met Your Mother' has featured some strongly meta casting in the past eight years, but little that warmed our hearts as much as seeing former 'Buffy the Vampire Slayer' couple Seth Green and Alyson Hannigan reunited for Monday's upcoming episode "The Final Page." We saw a picture of the reunion earlier, but are you ready to see Willow and Oz together again for real? Check out the latest clip!

Short of recruiting Sarah Michelle Gellar or Amber Benson, Seth Green's upcoming appearance on 'How I Met Your Mother' might be the show's best 'Buffy' reunion yet. The nerd culture 'Robot Chicken' creator will guest on this coming Monday's first hour-long episode "The Final Page" as Daryl, a forgotten friend of Lily and Marshall's from their college days.

Problem is, poor Daryl hasn't let go of the idea that the three are still best friends! TVLine has the first official clip from the episode, which reunites the former 'Buffy' stars and puts our beloved gang in a rather terrifying position in Daryl's basement. But what secrets could the peppy college chum have? What happened to Barney's voice? And is anyone else painfully aware how much Jason Segel sticks out among Joss Whedon fan-favorites?

Check out the 'Buffy' reunion of Seth Green and Alyson Hannigan in the clip from 'How I Met Your Mother's mid-season finale "The Final Page," and give us your predictions in the comments!